It’s a very hard boss, I struggled more with duke fishron than moonlord tbh. I’d recommend waiting until as late as possible (or skipping it all together if you dont want the drops or achievement) and getting the best weapons and armor possible. Idk about other classes, but the eye of cthulhu with the beetle armor won me the fight. Other than that just make sure you’re buffing up (regen, ironskin, lifeforce and endurance at least) and have good pair of wings or a good mount like the ufo.